Can you confirm whether you have a 5400rpm or 7200rpm drive?
As for an upgrade, it really depends on your needs. An SSD would be great for a boot drive, even a budget SSD... ~$60-$70.
Provided your HDD is is not failing, you could use the two together.
If however, the HDD is failing & you need to replace, you'll need to consider storage space vs speed.
SSDs are faster, but are much more expensive on a $ to GB basis.
A 1TB HDD (7200rpm) is ~$50, a 240ishGB SSD is a minimum $60ish.